Performance Evaluation of LDPC-Coded SISO-OFDM Adaptive Modulation and Coding under Rayleigh/Rician Fading and Power Amplifier Nonlinearity

Abstract

In this paper, a controlled link-level evaluation of a manually decoded low-density parity-check (LDPC)-coded single-input single-output orthogonal frequency-division multiplexing (SISO-OFDM) system with adaptive modulation and coding (AMC) is provided in two frequency-selective fading environments: Rayleigh and Rician fading, with and without a memoryless Rapp power amplifier (PA). The contribution is a fading law-based, repeatable estimation of the shift of the BER calibrated modulation and coding scheme (MCS) activation thresholds as a result of the transmitter nonlinearity, using the same physical layer decoder curves for calibration and evaluating the AMC in the presence of delayed/noisy feedback. The final study is conducted using a SNR range of 0-39 dB in 0.25 dB steps, a target for BER of 10-3, confirmation (2 consecutive points), an activation margin of 0.25 dB, a number of Monte-Carlo frames of 400-800 per fixed-MCS/step and a Doppler-correlated AMC trace of 5000 frames. The activation threshold At 256-QAM, R=2/3, Rician fading lowers the activation threshold from 37.00 to 30.25 dB without PA and from 38.25 to 31.25 dB with PA. The PA changes this threshold by 1.25 dB when it is used in Rayleigh fading and by 1.00 dB when it is used in Rician fading at 7 dB input back-off. At 39 dB, AMC goodput is 41.73, 39.33, 44.80, and 44.75 Mbit/s for Rayleigh/no-PA, Rayleigh/PA, Rician/no-PA, and Rician/PA, respectively. The observed results indicate that the PA penalty at this back-off is manifested primarily as a delay in the activation of high-order MCS, instead of the loss of the highest MCS at the higher end of simulated SNR range.